Piping systems in mining operations (including the oil sands mining industry) are used to transport mixtures of solid rock and sand particles in a liquid or slurry to a processing plant and to recycle debris back to the mining area or to a storage area. Current slurry hydro-transport pipes are typically made from low carbon, pipeline grade steel (e.g., API specification 5 L X65 or X70 grade steels). These pipes are subjected to significant abrasive/erosive wear and corrosion that causes wall loss and leads to frequent repairs and replacements. As such, these piping systems are often the source of significant operational costs for mining projects. There are significant economic incentives to develop pipe materials with improved erosion/wear/corrosion resistance.
There also exists a need for enhanced wear resistant steel in the oil sands mining industry. Such oil sands deposits have been commercially recovered since the 1960's, and the recovery rate has grown in recent years. Bitumen ore has generally been extracted either by surface mining techniques for shallow deposits (e.g., less than 100 m depth), or by in-situ thermal extraction (e.g., involving the injection of steam, chemical solvents and/or mixtures thereof) for deep deposits located deeper underground (e.g., around 100 m or deeper). For the surface mining of shallow oil sands, many types of heavy equipment and pipelines are utilized. First, the oil sands are typically excavated using shovels which transfer the mined material to trucks/vehicles. The vehicles move the oil sand ores to ore preparation facilities, where the mined ore is typically crushed and mixed with hot water. The oil sands slurries are then typically pumped through hydro-transport pipelines to the primary separation cell (PSC), where the oil bitumen is generally separated from the sand and water. After the bitumen is separated, the remaining sand and water slurry is then transported through tailings pipelines to tailings ponds for sands to settle down. The hydro-transport of large amounts of slurry mixture causes significant metal loss in conventional metallic pipelines or the like, which results in short replacement cycles and considerable operational costs.
Thus, the oil sands mining and ore preparation processes involve several stress and/or impact abrasion challenges in multiple equipment/operational areas (e.g., shovel teeth, hoppers, crushers, conveyers, vibrating screens, slurry pumps, pipelines, etc.). For example, in the downstream slurry transportation and extraction processes, some of the challenges encountered in the equipment, pipelines (e.g., hydro-transport pipelines), pumps and/or the PSC include erosion, erosion/corrosion, corrosion, stress, wear and/or abrasion or the like of the equipment/materials. These equipment/material erosion/corrosion challenges or the like lead to significant repair, replacement and/or maintenance costs, as well as to production losses.
As noted, current piping structures for slurry hydro-transport are typically made from low carbon, pipeline grade steel (e.g., API specification 5 L X70 in 45th edition). In general, fast moving solids in the slurry flow can cause considerable metal loss from the pipes (e.g., metal loss of the inner pipe wall). The aqueous and aerated slurry flow also typically cause accelerated pipe erosion by creating a corrosive environment. Moreover, particulate matter in the slurry (under the influence of gravity) causes damage along, inter alia, the bottom inside half of the pipes. For example, the hydro-transport and tailings pipelines that carry the sand and water slurry in oil sands mining operations undergo severe erosion-corrosion damage during service, while the bottom part (e.g., at the 6 o'clock position) of the pipeline typically experiences the most severe erosion wear.
In order to extend the service life of the pipelines some mine operators have utilized the practice of periodically rotating pipelines. For example, the pipelines are occasionally rotated (e.g., after about 3000 hours of service) by about 90°. After about three rotations (e.g., after about 12000 hours of service), the pipelines are typically fully replaced. Various materials, such as martensitic stainless steels, hard-facing materials (e.g., WC-based, chromium-carbide based), and polymer lining materials (e.g., polyurethane), have been evaluated and used by oil sands mining operators. However, such materials have found only niche applications, typically due to either relatively poor wear/erosion performance (e.g., polymer liner), high material/fabrication costs (e.g., WC-based hard metal, chromium-carbide based hard metal overlay material), or limited available thicknesses (e.g., bi-metallic multi-layer hardened steel materials). Pipe erosion and the like remains a serious problem, and alternative pipe structures and/or materials are sought to allow for a more efficient/economical operation/solution.
Improved steel compositions having enhanced erosion/wear/corrosion performance have been developed recently to reduce operational costs in mining operations. Specifically, improved high manganese (Mn) steel with enhanced wear/erosion/corrosion resistance has been developed for oil sands mining applications, including slurry pipes. In order to be successfully implemented, high Mn steel slurry pipe sections must be joined together in the field to create high Mn steel slurry pipelines. Slurry pipelines are constructed using several different types of joining methods, including: girth butt welds, flanges, and mechanical couplings. The girth butt welds used to join high Mn steel slurry pipes sections directly to one another need to provide the required strength, toughness and wear properties and also should be applied during field construction without undue concern regarding “weldability” or ease of application. A girth butt weldment joining high Mn steel slurry pipe sections will be exposed to the internal slurry service fluids and solids and therefore must meet or exceed the erosion/corrosion performance of the pipe base metal in order to achieve maximum benefit of applying high Mn steel for the slurry pipe application.
High Mn steel weld metals developed to date are not sufficient for joining erosion resistant high Mn steel slurry pipelines. Conventional high Mn steel consumables used to weld cast Hadfield steel (commonly used in railway components) do not provide sufficient weld metal strength to be used to join the recently developed erosion resistant high Mn steel slurry pipes. High Mn steel welding consumables used for hard facing applications cannot consistently provide the required weld metal toughness levels for, for example, slurry pipeline girth welds.
U.S. Patent Application Publication No. 2013/0174941 describes high Mn steel developed for cryogenic applications such as storage containers for liquefied natural gas (LNG). Weld metals have been developed for cryogenic high Mn steel, such as those described in J. K. Choi, et al, “High Manganese Austenitic Steel for Cryogenic Applications”, Proceedings of the 22nd International ISOPE Conference, Rhodes, Greece 2012. These cryogenic high Mn steel weld metals, while providing sufficient toughness at very low temperatures down to −200° C., do not provide adequate weld metal strength for the erosion resistant high Mn steel when used for, for example, slurry pipe applications.
Thus, a need exists for welding technology that can be used to construct, e.g., high Mn steel slurry pipelines for oil sands mining projects that simultaneously produces adequate strength, adequate toughness, and high erosion/corrosion resistance that can be applied during high Mn steel pipeline field construction without undue concern regarding weldability or ease of use.